1. Field of the Invention
The present invention relates to a method and a device for modifying a standard model. The invention is useful for generating a three-dimensional model in the field of computer graphics, for example.
2. Description of the Prior Art
In recent years, the three-dimensional CG (three-dimensional computer graphics) technique is often used in the fields of movies, games and so on. In the three-dimensional CG, a three-dimensional model, a light source, etc. are located and moved in a virtual three-dimensional space; therefore, the three-dimensional CG is high in the degree of freedom of expression.
Conventionally, a non-contact three-dimensional measurement device employing the light-section method has been put into practical use. Three-dimensional data of an object can be relatively easily obtained by using such non-contact three-dimensional measurement device. However, various problems have been detected in using the three-dimensional data obtained by means of the non-contact three-dimensional measurement device as it is for three-dimensional CG. For example, it is necessary to reduce the amount of data obtained by the measurement by a process of thinning the data, which is complicated and time-consuming.
To solve the above problems, there has been proposed a method wherein a standard model is prepared for an object and the standard model is modified in accordance with three-dimensional data of the object obtained by an actual measurement of the object (Japanese Unexamined Patent Publication No. 5-81377).
In the above-mentioned method, three-dimensional shape information of the three-dimensional data obtained by the measurement, i.e., a point group (a group of points) in the three-dimensional space, is used as an object for fitting, and a surface of the standard model is fitted on the three-dimensional point group.
Although a general shape of an object can be reproduced according to the above method, it is difficult to reproduce topical characteristics of a shape of the object.
For example, in the case of making a three-dimensional model of a human head according to the above method, although a general shape of the resulting three-dimensional model conforms to an object for measurement, i.e., the human head, parts that influences much for expression of the face such as eyes, mouth and the like do not satisfactorily conform to those of the object. Thus, it has been difficult to represent delicate expressions of a human.
Further, when two-dimensional image information is used for reproducing an outline, characteristics, etc. of a face, a topical modification occurs in the standard model thereby causing an improper modification.
For generating a three-dimensional model of human head, a preformed standard model of human head is typically fitted to three-dimensional shape data obtained by measuring a human head.
Human head, in general, consists of a face and hair. Three-dimensional measurement of the face is easy, while that of the hair is difficult. Accordingly, there is a problem in the above-mentioned fitting of the standard model that a part of the hair does not fit to the three-dimensional shape data satisfactorily.
In the aforementioned prior art, operations for modifying a surface of the standard model in accordance with measured three-dimensional points are time-consuming due to the large quantity of data to be operated.
If number of the three-dimensional points is decreased for the purpose of data reduction, a three-dimensional model to be generated is low in precision with making it difficult to express delicate expressions of a human. On the other hand, if the number of the three-dimensional points is increased too much, a topical modification may occur in fitting a standard model, thereby degrading a shape as a whole.